Echometer M, Manual, Page: 42 / 45

Echometer Company
Model – M Manual
Phone: (940) 767-4334
5001 Ditto Lane Page 42 Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A. E-Mail:CARBON DIOXIDE INFORMATION (CO
2
)
Carbon dioxide is a nonflammable, colorless, odorless, slightly acid gas. It is one and one-half times as heavy as air. CO
2
is
used in the carbonation of soda pop, as an inert agent in fire extinguishers, in canned food products, and many other
applications.
Below 88
o
F, confined CO
2
liquid and gas are in equilibrium at a vapor pressure shown in the table below. For example, a
Cylinder of CO
2
liquid and gas at 59
o
F has a pressure of 723-psia. As gas is removed from the cylinder, the liquid vaporizes
into a gas, which maintains the vapor pressure shown. When all of the liquid has been vaporized, the gas pressure will reduce
as gas is withdrawn. Following is a table of the vapor pressure as a function of temperature.
Temperature Pressure
o
F
o
C PSI Bar
88 31 1053 73
59 15 723 50
32 0 490 34
5 -15 317 22
-22 -30 192 13
Above 88
o
F, CO
2
becomes a fluid. Liquid does not exist separate from gas. The pressure in the tank is an indication of the
amount of CO
2
present in the tank. As the gas is used, the pressure will decline. At 90
o
F, the pressure in a full cylinder will
be approximately 1100-psi.
The amount of CO
2
in a cylinder is determined by weighing the cylinder containing the CO
2
and then subtracting the weight of
the empty cylinder which is shown on the cylinder. Below 88
o
F, the amount of CO
2
in the cylinder cannot be estimated by
measuring the pressure unless the pressure is less than the vapor pressure shown on the graph. If the pressure is less than the
vapor pressure, the Cylinder does not contain any liquid CO
2
and very little CO
2
remains in the Cylinder.
CO
2
is heavier than air and may collect in confined, unventilated areas. Do not permit a leaking cylinder in a closed
automobile. CO
2
is the regulator of the breathing function, and an increase in the CO
2
inhaled will cause an increased rate of
breathing. In high concentrations, CO
2
can paralyze the respiratory system. Do not breathe air having excessive amounts of
CO
2
.
Do not overfill a CO
2
Cylinder or dangerous pressures can result. Do not use CO
2
cylinders, which show any sign of wear,
abuse, corrosion, worn threads or any mishandling.
PHYSICAL CONSTANTS
Density, Gas @ 70
o
F, 1atm 0.1146 lb/cu ft
Critical Temperature 87.8
o
F (31
o
C)
Critical Density 0.468 g/ml
Critical Pressure 1072-psia (73-atm)
Specific Gravity 1.53
Specific Volume @ 70
o
F, 1-atm 8.76 cu ft/lb
or 15,000 cu in/lb
or 950 cu in/oz